Dark pixels are used in light sensing and imaging devices to compensate for signal components that are generated by causes other than light falling on a light sensor. These signal components may be referred to as dark current. To compensate for the dark current, one or more light sensors (also known as pixels) are prevented from receiving any light. These may be referred to as dark pixels. To compensate for the dark current, the outputs from the dark pixels may be subtracted from the outputs of the light receiving pixels to remove a component of the dark current from the outputs of the light receiving pixels.
To form a pixel, a photoelectric device is fabricated with a transparent layer. This transparent layer typically allows light to pass through to a light sensing region while still being conductive. By still being conductive, the transparent layer may be patterned and used as an electrode or other conductor in the formation of the light sensing or imaging device. This transparent layer may be selected from a group that includes indium tin oxide (ITO), indium oxide, tin oxide, zinc oxide, cadmium oxide, cadmium tin oxide, titanium oxide, and gold thin film.
To form a dark pixel, the light-receiving region of a pixel is covered with a light shielding layer that prevents that pixel from receiving light. Prior art devices have constructed this light shielding layer from Aluminum (Al) or an Aluminum alloy such as Al--Si, Al--Ti, Al--Cu, Al--Si--Ti and Al--Si--Cu, or others.
Unfortunately, when it is desirable to place the light-shielding layer over the transparent layer, patterning these light-shielding materials is difficult. Extra processing steps and photomasks may be required to avoid damaging the ITO when the light shielding layer is etched using typical etchants for these materials. Accordingly, there is a need in the art for a light shielding layer that may be easily etched without etching the ITO.